Sometimes minor characters are based on people I know — Simon’s friends Eric, Kirk and Matt are all friends of mine. But I’m not writing a thinly veiled version of my own life. These characters are created to fit the needs of the story and to be very much themselves. Sometimes they incorporate aspects of people I know, or have met, like Simon’s sense of humor or Clary’s artistry. Jace, alas, is definitely not based on anyone real.
As for the places in the books, obviously Idris and environs are entirely made up. Most of the Manhattan locations — the Pandemonium Club, the Institute, Garroway’s Books, The Dumont Hotel,Taki’s, are in real places, but don’t actually exist there. The Marble Cemetery (the City of Bones) does exist in some form http://www.marblecemetery.org/ , and the Renwick Smallpox Hospital is a real place.